that appears in the upper-right corner of the attachment, then choose Markup. Or simply 
Sketch a shape using a single stroke.
If your drawing is recognized as a standard shape, it’s replaced by that shape; to use your drawing instead, choose it from the palette that’s shown.
Draw 
: Drag the highlight where you want. To resize it, use the blue handles.
Text 
(it appears to the right of the signature). The signature is no longer available to use in any app where you can add a signature.
Shape Style 
Change the font or the font style and color.
Rotate Left 
until you’re done rotating the item.
Crop 
, 
, then choose a device. The tool may appear highlighted to show your device is connected. To disconnect your device without using it, click the tool again.
Note: To use your nearby iPhone or iPad to sign or annotate items, it must meet Continuity system requirements. See the Apple Support article Create and use email signatures in Mail on Mac